In recent years, as wireless networks play a more and more important role in modern people's life, users' requirements on performance of the wireless networks become increasingly higher. Correspondingly, various technologies for improving the network performance have been developed. Among these technologies, the multi-input multi-output (MIMO) antenna technology is considered as an important technology because of such advantages of extended network communication coverage, improved connection quality, improved spectrum efficiency and a high data rate.
In particular, according to the MIMO antenna technology, multiple sets of antennae are disposed in a communication apparatus and signal transmissions are accomplished through a corresponding protocol. In other words, because the communication apparatus adopting the MIMO antenna technology is provided with multiple sets of hardware antennae, signal transmissions must be coordinated according to configurations of the hardware antennae when the communication apparatus is to transmit signals. In order to make the coordination between signal transmissions more efficient, a channel feedback mechanism is usually established between communication apparatuses operating in a wireless network that adopts the MIMO antenna technology so that the communication apparatuses can transmit information in a more efficient way. In the prior art, the channel feedback mechanism is typically accomplished in two ways, namely, the precoder matrix indicator (PMI) feedback and the sounding-based feedback.
In more detail, the PMI feedback mainly operates in the following way. A plurality of precoder matrices are predefined between a communication apparatus at a transmitting end and a communication apparatus at a receiving end. When the communication apparatus at the transmitting end and the communication apparatus at the receiving end are to communicate with each other via a channel, the communication apparatus at the receiving end may choose one of the precoder matrices that is appropriate for transmitting a signal according to channel conditions, and notify the chosen precoder matrix to the communication apparatus at the transmitting end. In this way, the communication apparatus at the receiving end and the communication apparatus at the transmitting end can perform signal transmissions therebetween by use of an identical precoder matrix.
Briefly speaking, the PMI feedback mainly utilizes predefined signal transmission configurations to perform signal transmissions. However, because the PMI feedback utilizes the precoder matrices in fixed configurations to perform signal transmissions, it cannot completely adapt to the channel conditions of the communication apparatuses and this leads to serious degradation in performance of the signal transmissions.
On the other hand, the sounding-based feedback mainly operates in the following way. The communication apparatus at the transmitting end transmits a sounding signal to the communication apparatus at the receiving end so that the communication apparatus at the transmitting end can determine uplink (from the receiving end to the transmitting end) channel conditions according to the sounding signal; meanwhile, the communication apparatus at the transmitting end can also estimate downlink (from the transmitting end to the receiving end) channel conditions according to the channel reciprocity. In this way, optimized signal transmissions can be performed by the communication apparatus at the transmitting end.
However, because the sounding-based feedback relies on the channel reciprocity to estimate the downlink channel conditions according to the uplink channel conditions, it is only applicable to environments where a channel reciprocity exists between the uplink channel and the downlink channel (e.g., Time Division Duplex (TDD) systems). Further speaking, because an uplink channel and a downlink channel in a Frequency Division Duplex (FDD) system may be within different frequency bands, a communication apparatus at the transmitting end in the FDD system might fail to estimate the downlink channel conditions according to the uplink channel conditions.
Accordingly, an urgent need exists in the art to provide a solution that can accomplish the channel feedback accurately and effectively in an MIMO network so as to perform signal transmissions in a more efficient way.